Illuminated dial plate



Nov. 13, 1956 DRQS YILLUMINATED DIAL PLATE Filed Jan. 9, 1952 INVENTQR ARIS DROS .& l) A J AG ENT ILLUMINATED DIAL PLATE Application January 9, 1952, Serial No. 265,683 r 1 Claims priority, application Netherlands February 12, 1951 2 Claims. (Cl. 240 2.1

This invention relates to improvements in dials having a dial plate of transparent material which areparticularly useful in radio receivers.

Use is frequently made, particularly in radio receivers, of dial plates of transparent material, illuminated by one or more incandescent lamps, the light of which falls through one of the edges in the plate in which it is propagated by total reflection.

Although initially the dial plates were always made of glass, there is an increasing use of dial plates of transparent plastic material, such, for example, as polymethacrylate.

Plastic dial plates, however, often give rise to difliculties due to the heat produced by the dial lamp, which may result in weakening and, after some time, dim-ness of the plastic material. Previously, this has been an o'bjection to the use of particular plastics having definite advantages, for example, polystyrene, the price of which is relatively low.

The invention has for its object to obviate these difiiculties, which are in general inherent with the use of dial plates of a material having little resistance to heat. This is eifected by providing a connecting piece between the incandescent lamp and the dial plate, this piece being made of a transparent material which has greater resistance to heat than the material of the dial plate.

The difliculties described above will be explained more fully with reference to the drawings in which:

Figure 1 shows the front view of a radio receiver according to the invent-ion.

Figure 2 is a perspective view of the invention from the rear side of the dial, and

Figure 3 shows in section another embodiment of the invent-ion.

The receiver shown in Fig. 1 comprises a front wall which comprises, as usual, a frame 1 having a board provided behind the aperture, in which an aperture 3 for the loudspeaker is provided and covered by a cloth. In front of this cloth provision is made for a dial plate 15 in suitable grooves of the frame 1, a pointer 7 being adapted to move behind this plate. In the connecting piece 17 provision is made for a recess 9 and an illuminating lamp III, which is arranged in a manner such that its light falls laterally on the connecting piece 17 and emerges at the markings of the station dial, so that these marks are distinctly illuminated.

With the use of dial plates of poorly heat-resistant material, for example plastic, in the device described above difiiculties are experienced .due to the heat produced by the lamp 11. Since most clear plastics are thermoplastic, i. e. they weaken under the action of heat, undue deformations and even often dimness of the material may occur about the lamp and over the lamp, hindering the transition of the light into the dial. This is undesirable from an aesthetic point of view. If, in order to avoid this etfect, the radius of the semi-circular recess 9 and hence the spacing between the lamp and the dial plate is chosen to be greater, the quantity of light nited States Patent 2,770,712 Patented Nov. 13, 1956 falling into the dial-plate is considerably reduced. Use may be made of plastics having a slightly greater heat resistance, such for example, as polymethacrylate, but they are materially more costly than plastics having low weakening temperatures, such as for example, polystyrene.

Fig. 2 illustrates, viewed from the rear side of the dial, howthe major part of the dial can be made of inexpensive plastic according to the invention. In this case, a trapezoidal connecting piece 17 of transparent sheet material is arranged between the vertical dial plate 15, made for example, of polystyrene, and the incandescent lamp 11, at right angles to the plate'1 5. The transparent sheet material in piece 17 has a higher weakening point than polystyrene and can be for example, polymethacrylate or glass. The incandescent lamp 11 is housed in a recess at the short parallel edge of the trapezoidal (horizontal) connecting piece 17 and the long parallel edge loosely engages the lower edge of the plate 15 or is secured thereto with the use of transparent adhesive.

Rays emanating approximately horizontally from the lamp 11 are collected by the connecting plate 17 and propagated to the lower edge of the dial plate 15. The rays fall on the rear side in a horizontal direction into the plate 15; however, on the front side, at the lower edge, the plate 15 has a facet, i. e. a slanting surface 19, which is at an angle of approximately 45 to the rear side of the plate and which reflects the horizontal incident inside of the plate approximately in a vertical direction.

As may be seen from the figure, the plate 15 is insulated from the heat produced by the incandescent lamp 11. In the arrangement described above, the cooling of the incandescent lamp is particularly favorable, since a vertical flow of air can freely brush past the lamp. In contradistinction to apparatus of the kind known, structural advantage is obtained by the present invention since the dial occupies little space and since the plate 17 extends primarily along the bottom of the cabinet. The trapezoidal intermediate piece ensures furthermore a uniform distribution of the light in the plate 15.

Furthermore, as an alternative, the plate 17 can be made of two plates of this kind and may be arranged in line with the plate 15.

The intermediate piece 17 may have a particular color or differently colored parts, so that a color effect may be obtained in a colorless dial plate.

Fig. 3 shows, in an axial sectional view, a second embodiment of the intermediate piece 21, which is, in this case, primarily rod-shaped; one end thereof may be secured in a fitting circular aperture in the dial plate 23. This is possible since the material of the plate 23 weakens at a lower temperature than that of the rod 21. At the free end, the rod has a cup-shaped cavity 24, in which the incandescent lamp 11 is housed. At the other end secured in the plate 23, the rod has a re-entrant profile 25 of such a shape that primarily axially incident light rays are projected into the plate 23 in radial directions. This construction is particularly suitable for dial plates, with which the incandescent lamp is arranged approximately opposite the center of the dial plate.

What I claim is:

l. A dial for use in radio receivers comprising an incandescent lamp, a transparent dial plate composed of a thermoplastic resin material which will be deformed or discolored when positioned adjacent to said lamp, said dial plate having a bottom marginal edge which slants angularly upwards, and a transparent connecting piece arranged between said lamp and said dial plate and angularly thereto, said piece being adapted to transmit light from said lamp to said dial plate through said bottom marginal edge and said piece being composed of a thermoplastic resin material exhibiting a value of resistance to heat at which said piece is not substantially deformed or discolored when adjacent said lamp.

2. A dial for use in radio receivers comprising an incandescent lamp, a transparent dial plate composed of a thermoplastic resin material which will be deformed or discolored when positioned adjacent to said lamp, said dial plate having a bottom marginal edge which slants angularly upwards, and a transparent connecting piece in the form of a trapezoidal plate arranged between said lamp and said dial plate and angularly thereto, said piece being adapted to transmit light from said lamp to said dial plate through said bottom marginal edge, said piece being composed of a thermoplastic resin material ex hibiting a value of resistance to heat at which said piece is not substantially deformed or discolored when adjacent said lamp and having a recess in the shorter parallel edge in which is located said incandescent lamp, the longer parallel side of said connecting piece engaging said dial plate, and the air heated by said lamp being adapted to escape in a substantially vertical direction without contacting said connecting piece.

References Cited in the file of this patent UNITED STATES PATENTS 1,714,242 Del Riccio May 21, 1929 2,071,284 Hy1and Feb. 16, 1937 2,150,836 Lamb Mar. 14, 1939 2,413,848 Simpson Ian. 7, 1947 2,560,117 Mallary July 10, 1951 2,611,018 Thorp Sept. 16, 1952 FOREIGN PATENTS 595,003 Great Britain Nov. 25, 1947 OTHER REFERENCES Proceedings of the I. R. E., December 1945, page 829, Table VIII. 

